Hampstead Tube station has some of the most polluted air on the London Underground, a report has revealed.

The research by the Committee on the Medical Effects of Air Pollutants (COMEAP) found the there was high levels of PM2.5 particles at Hampstead station. In November 2015, an average 492 micrograms per cubic metre (μg/m3) of air was recorded by surveyors.

The samples were collected every four hours over a two-day period at the station on the Northern Line. The work was commissioned by Transport for London.

The report published yesterday said the mass concentration of the particulates underground is much higher than would be seen above ground. It said the ambient PM2.5 annual mean concentration measured at a roadside monitoring site close to a busy road in London was 16 μg/m3.

PM2.5 particles are fine particulates produced during the burning of solid and liquid fuels. Long-term exposure is linked to cardiovascular problems, as well as heart and lung conditions.

According to TfL, London Underground operates well within the Health and Safety Executive specified limits and recently “informally adopted” stricter recommendations to cut down particles on the Tube.

Professor Frank Kelly, who chairs COMEAP said further testing was needed, but people should continue to travel on the network.

He said: “It has not been possible to estimate the health risks from particulate matter air pollution for people travelling on the London Underground because the particles arise from different sources and have a different chemical composition to those found in most studies. However, there is no convincing evidence that Underground particulates are more toxic than those found outdoors.

“Given that there is strong evidence that exposure to particulates outdoors is harmful, it is likely that there is some health risks associated with exposure to Underground particulates.”

The transport authority axed a “cleaning train” in 2014 after finding it ineffective. It now cleans lines using industrial vacuums and “magnetic wands.”

TfL said it accepted the reports, and will carry out further testing. The next samples will be taken in the next few months.

Peter McNaught, director of asset operations at TfL said: “It is vital that we operate with the very latest understanding of the risks arising from particles in the air, which is why we commissioned COMEAP to undertake this research. Although the report emphasises further monitoring and research is needed, it is an important contribution to the study of health effects associated with dust exposure.”

“We are committed to maintaining the cleanest air possible for our staff and customers when using the Tube. We closely monitor dust levels on the Tube and, through a wide range of measures, ensure that particle levels are well within Health & Safety Executive guidelines. We have already enhanced our sampling regime by including tests for additional metals and we will continue to investigate ways we can keep dust and particles to an absolute minimum.”